The present invention relates generally to cell planning and, more particularly, to the automated systems for determining neighbor lists and PN offsets for newly deployed cells and/or sectors.
In Wideband Code Division Multiple Access (WCDMA) networks, pilot signals transmitted by different base stations and sectors are distinguished by the use of different phase offsets of the same pseudorandom noise (PN) sequence. The PN offset enables the mobile terminals to differentiate between different sectors when implementing cell search algorithms for mobility management purposes. Conventionally, a network administrator assigns the PN offsets to the sectors within a network so that neighboring sectors do not have the same PN offset. The main goal is to prevent interference or aliasing with other sectors in the area. However, as network operators increase the number of sectors to provide better coverage, it becomes increasingly difficult to avoid conflicts.
There are currently two existing methods for determining PN offsets for new sectors that are widely used in the industry. A first method uses radio frequency (RF) propagation prediction software to estimate interference between sectors. The PN offset with the least network impact is chosen as the PN offset for the new sector. This method has drawbacks related to using estimation methods as opposed to actual measurements of conditions. Furthermore, neighbor list information is not always considered and no PN conflict calculations are made. A PN conflict is occurs when 1) at least two different sectors are serving a common area with an identical PN offset, or 2) the neighbor list of a sector contains of at least two neighbor sectors with an identical PN offset.
A second method commonly used is based only on analysis of a neighbor list. This method begins with a list of possible PN offsets and uses the neighbor list to eliminate first second and third degree neighbors. This method does not take into account mitigating factors such as distance and terrain, and, consequently, may result in the elimination of many PN offsets that would be acceptable. The result is a reduced candidate set which makes it very difficult to find PN offsets in areas with many cell sites, such as a typical metro downtown.
There are also two commonly used methods for determining a neighbor list for a new sector. The RF prediction method is used to populate the neighbor list of a new sector with x (e.g., 15, 20, etc.) sectors that have the strongest signal in the coverage area of the new sector. This method does not rely on actual RF measurements and that alone makes the initial neighbor list inaccurate in most cases. The second method involves using a map and visually selecting the nearest sectors to determine the a neighbor list. The second method does not use all network information available and also relies on the user to include factors such as terrain to come up with an initial neighbor list.
Accordingly, there is a need for improved methods to more accurately determine a neighbor list and PN offset for a newly deployed sector in a mobile communication network